1. Field of the Invention
The present invention relates to a mask lithography data generation method for manufacturing an electron beam exposure mask that is used when manufacturing a semiconductor device, and in particular to a mask lithography data generation method for lithography by a vector-type electron-beam exposing apparatus.
2. Description of the Related Art
During the manufacturing process of a semiconductor device, a process that forms the components of the semiconductor device by forming a pattern of a predetermined form in a thin conducting or insulating layer is performed as follows. First, a thin layer that is to be processed is formed. A resist is then formed as a layer on this thin layer and the resist is selectively exposed through electron beam (EB) lithography (wafer lithography) using a mask in which the predetermined pattern has been formed. After this, the resist is developed to selectively remove parts of the resist, thereby forming a resist pattern. The thin layer is then selectively removed by means such as etching with the resist pattern as a mask.
The mask used in wafer lithography mentioned above is also manufactured by EB lithography (mask lithography). In more detail, a resist is formed on a mask material, a pattern is drawn in the resist by an electron beam, and then the resist is developed to remove parts of the resist and so form a pattern. Means, such as etching or the like, is then used to selectively remove parts of the mask material, with the resist in which the pattern has been formed as a mask. By doing so, a mask in which a predetermined pattern has been formed is produced.
With the high integration of semiconductor devices in recent years, the patterns formed on wafers are becoming increasingly fine. As one example, the smallest dimensions for forming patterns are in the process of switching from 0.18 xcexcm to 0.10 xcexcm. As a result, the masks used of EB lithography need to be made increasingly fine.
When the masks used for EB lithography are made fine, however, there is the problem of the proximity effect causing decreases in the formation precision of the resist pattern. FIG. 1A is a plan view showing one example of a mask that is used during conventional EB lithography (wafer lithography), while FIG. 1B is a plan view showing the form of a resist pattern that is formed by this mask. FIG. 2 is a plan view showing the form of the mask after correction. As shown in FIG. 1A, the mask 61 is provided with an opening 62. The width A of the opening 62 is 400 nm, for example. When another opening, opening 63, is formed at a position next to the opening 62 and a resist pattern is formed by performing lithography using the mask 61 with a projection magnification on the wafer of (xc2xc) times, for example, the form of the resist pattern 64, which corresponds to the opening 62, is not a resemblance 62a of the opening 62, and ends up narrower than the resemblance 62a, for example.
For this reason, the form of the opening 62 formed in the mask 61 is conventionally corrected in advance to become the opening 62b, as shown in FIG. 2. The form of the opening 62b is produced by adding a corrective part 62c to the original opening 62. The opening 62 may be 400 nm wide, for example, and the corrective part 62c may be 20 nm wide, for example. When lithography is performed at a projection magnification of (xc2xc) times using this mask 61, in the resist pattern formed on the wafer, the width of the region corresponding to the opening 62 is 100 nm, and the width of the region corresponding to the corrective part 62c is 5 nm.
EB exposing apparatuses include raster-type EB exposing apparatuses that perform lithography by scanning an electron beam and vector-type EB exposing apparatuses that divide a pattern into rectangles and shoot an electron beam separately at each rectangle. Of these, vector-type EB exposing apparatuses are capable of drawing with higher precision, so that vector-type EB exposing apparatuses are used when producing a mask by forming a fine pattern in a mask material. In order to manufacture a mask using a vector-type EB exposing apparatus, it is necessary to generate mask lithography data, in which the pattern for forming the mask is divided into rectangles, in advance. A mask is then manufactured by performing EB lithography (mask lithography) on a mask material based on this mask lithography data.
FIG. 3A and FIG. 3B show a method of dividing the opening 62b. When EB lithography is performed using the mask 61 (see FIG. 2) in which the opening 62b has been formed, an electron beam is shot with the opening 62b having been divided into rectangles. As shown in FIG. 3A, one example of how the opening 62b can be divided divides the opening 62b into the opening 62 and the corrective part 62c. However, if the corrective part 62c is narrow, there is the problem that the width precision of the EB lithography falls.
FIG. 4A and 4B are graphs showing the influence of the width of a rectangle produced by the division on the EB output characteristics, with the horizontal axis showing positions in the horizontal direction in a divided rectangle and the vertical axis showing the EB output. FIG. 4A shows the case of a rectangle whose width X is large, while FIG. 4B shows the case of a rectangle whose width X is small. As shown in FIG. 4A, when the width X of a rectangle is large, for example, 25 nm or more on the wafer, an approximately equal EB output is obtained across the width direction. Conversely, as shown in FIG. 4B, when the width X of a rectangle is small, for example, below 25 nm on the wafer, the EB output at the ends of the rectangle is low, with the EB output in the central part of the rectangle also falling. This is to say, there is a drop in the EB output characteristics. For this reason, there is a drop in the width precision of the EB exposure, so that the formation precision of the mask pattern also falls, resulting in a drop in the formation precision for semiconductor devices.
Due to the above, it is necessary to shoot the electron beam having divided the opening 62b without forming a shape with a narrow width (hereafter referred to as a xe2x80x9cminute shapexe2x80x9d), such as that shown in FIG. 3A. As shown in FIG. 3B, dividing the opening 62b into the rectangles 68a, 68b, and 68c does not produce any minute shapes, so that there is no fall in the EB output characteristics. Conventionally, methods of generating lithography data that divide mask patterns in this way to avoid producing any minute shapes are used.
FIG. 5 is a block diagram showing a conventional mask lithography data generation apparatus. As shown in FIG. 5, the conventional mask lithography data generation apparatus 50 includes a rectangle division processing unit 52, a minute shape removal processing unit 53, and a mask lithography data converting unit 55. The following describes a conventional method of generating mask lithography data.
First, layout data 51 is generated. The layout data 51 is two-dimensional coordinate data showing the form of the opening 62b shown in FIG. 2, for example. Next, the layout data 51 is inputted into the rectangle division processing unit 52, and a rectangle division process is performed on the layout data 51. By doing so, a pattern corresponding to the opening 62b is divided as shown in FIG. 3A, for example, into a plurality of rectangles, or more specifically, the opening 62 and the corrective part 62c. At this point, the rectangle corresponding to the corrective part 62c has a narrow width, making it a minute shape.
Next, the layout data that has been subjected to the rectangle division process is inputted into the minute shape removal processing unit 53. By doing so, the pattern divided into rectangles as shown in FIG. 3A is redivided into rectangles as shown in FIG. 3B, so as to remove the minute shape (the part corresponding to the corrective part 62c) and generate xe2x80x9cminute shapelessxe2x80x9d data 54. After this, the minute shapeless data 54 is inputted into the mask lithography data converting unit 55, where the format of minute shapeless data 54 is converted into a format that can be recognized by a mask lithography apparatus (not shown in the drawings), thereby producing the mask lithography data 56. The mask lithography data 56 is inputted into the mask lithography apparatus, and lithography is performed with an electron beam based on the mask lithography data 56 to produce a mask.
However, the conventional technique given above suffers from the following problem. FIG. 6A shows the form of a resist pattern that is formed on a wafer, while FIG. 6B shows the form of an opening in a mask for forming the resist pattern 65 shown in FIG. 6A. It should be noted that the openings in the mask for forming the resist patterns 66 and 67 that are shown in FIG. 6A have been left out of FIG. 6B. As shown in FIG. 6A, the resist pattern 65 that is formed on the wafer is L-shaped. The part 65a of the resist pattern 65 is a region that corresponds to a gate electrode of a semiconductor device, for example. At a position close to the resist pattern 65, other resist patterns 66 and 67 are formed. As shown in FIG. 6B, the form of the pattern 41 for forming the mask that forms the resist pattern 65 is a combination of an L-shape 69, which is a resemblance the resist pattern 65, and corrective parts 70 and 71 for correcting the proximity effect.
FIG. 7A and FIG. 7B show the patterns of a mask, with FIG. 7A showing the pattern before division into rectangles and FIG. 7B showing the pattern after division into rectangles. The following describes the method whereby mask lithography data is generated using a conventional mask lithography data generation apparatus shown in FIG. 5, based on the pattern 41 shown in FIG. 6B.
First, as shown in FIG. 5, the layout data 51 is generated. The layout data 51 is two-dimensional coordinate data showing the form of the pattern 41. Next, the layout data 51 is inputted into the rectangle division processing unit 52. As a result, as shown in FIG. 7B, the pattern 41 is divided into the rectangles 43 to 46. At this point, the rectangles 43 and 44 are minute shapes.
Next, the layout data that has been subjected to the rectangle division process is inputted into the minute shape removal processing unit 53. Next, the minute shape removal processing unit 53 tries to remove the minute shapes from the pattern 41.
However, since the pattern 41 includes the minute corner part 42, no matter how the pattern 41 is divided into rectangles, a minute shape will always be produced, so that the minute shape removal processing unit 53 is unable to remove minute shapes from the pattern 41. This means that the rectangles 43 and 44 that are minute shapes are left in the mask lithography data 56, so that there is a drop in the EB output characteristics when lithography is performed using this mask lithography data 56. As a result, there is a drop in the precision of the lithography, and so a drop in the formation precision of the pattern formed in the mask.
This in turn causes a drop in the formation precision of the resist pattern 65 (see FIG. 6A) on the wafer. If, for example, the part 65a of the resist pattern 65 is a region corresponding to a gate electrode of a transistor in a semiconductor device, this means that there is a drop in the precision with which the gate electrode is formed. As a result, there is a drop in the characteristics, such as the operating speed, of the transistor.
It is an object of the present invention to provide a mask lithography data generation method for an electron beam exposure mask that is used when electron beam lithography is performed with a polygon-shaped pattern being divided into rectangles. This mask lithography data generation method is able to improve the formation precision of a pattern of the mask that corresponds to a region, in a semiconductor device, where formation precision is especially demanded, by removing minute shapes from the mask lithography data that corresponds to the region.
A mask lithography data generation method according to the present invention is a method for an electron beam exposure mask used in electron beam lithography where a polygon-shaped pattern is divided into rectangles. This mask lithography data generation method of the invention has the steps of: dividing layout data that shows a form of the pattern into selected region data for a selected region and unselected region data for an unselected region, the selected region being a part of the pattern that needs to be formed precisely and the unselected region being a part of the pattern that may be formed less precisely than the selected region; dividing the selected region data into a plurality of pieces of rectangle data by dividing the selected region into a plurality of rectangles whose shortest sides are longer than or equal to a reference value; and recombining the selected region data that has been divided into the plurality of pieces of rectangle data and the unselected region data.
With the present invention, the pattern for forming a mask is divided into a selected region and an unselected region, and the selected region is divided into a plurality of rectangles whose shortest sides have lengths that are longer than or equal to a reference value, so that even if minute shapes cannot be removed from the pattern as a whole, minute shapes can still be removed from the selected region. This means that by setting a region in a semiconductor device where formation precision is especially important, such as a region where a gate electrode of a transistor, a contact, a via hole, etc., is formed, as the selected region, a drop in the formation precision of this region can be prevented.
The mask lithography data generation method according to the present invention may also have a step of converting the recombined layout data into mask lithography data. By doing so, the layout data can be converted into data that can be recognized by a mask lithography apparatus.
It is preferable for the step that divides the selected region data into the plurality of pieces of rectangle data by dividing the selected region into the plurality of rectangles whose shortest sides are longer than or equal to a reference value to have the steps of: dividing the selected region data into a plurality of pieces of rectangle data by dividing the selected region into the plurality of rectangles using lines that join vertices of the selected region; combining some or all of the plurality of pieces of rectangle data to generate one or more larger pieces of rectangle data; and judging whether a length of a shortest sides in a rectangle represented by each of the larger pieces of rectangle data are longer than or equal to the predetermined value, with the step of dividing the selected region data into the plurality of pieces of rectangle data by dividing the selected region into the plurality of rectangles using the lines that join the vertices of the selected region, the step of generating the larger pieces of rectangle data, and the step of judging whether the length of the shortest sides are longer than or equal to the predetermined value being repeated when it is judged in the step of judging whether the length of the shortest sides are longer than or equal to the predetermined value that the length of the shortest side is below the predetermined value.
According to the present invention, in a mask lithography data generation method for an electron beam exposure mask used in electron beam lithography where a polygon-shaped pattern is divided into a plurality of patterns, minute shapes can be removed from mask lithography data that corresponds to a region of a semiconductor device where formation precision is especially required, so that the formation precision of the pattern of the mask that corresponds to this region can be improved.